Virulence Tests for Typhoid Bacilli and Antibody Relationships in Antityphoid Sera.

VARIATION and dissociation in the enteric group of bacteria are accompanied by changes in antigenic properties 1, 2, 3; and such changes may, in turn, affect the value of these variants or dissociants for prophylactic purposes. Relative virulence of these organisms also may be associated with dissociation and correlated with antigenic activity. The lack of sensitive and convenient methods for determination of virulence and of antibody relationships in antisera produced against typhoid bacilli of established virulence has led to the following experimental work. Particular emphasis has been placed on the measurement of protective action of the antisera in an attempt to determine whether there is a correlation of such activity with some known and easily determinable property of the antisera and whether this property may be correlated with antigenic components of the organisms being studied. Methods for determination of virulence of typhoid bacilli and for measurement of protective action of antityphoid sera are presented, together with preliminary data obtained by these methods.